Download Cognitive approaches to the development of short

Review
Gathercole – Development of short-term memory
Cognitive approaches to
the development of
short-term memory
Susan E. Gathercole
The capacity to retain information for brief periods of time increases dramatically during
the childhood years. The increases in temporary storage of speech-based material that
take place in the period spanning the pre-school years and adolescence reflect complex
changes in many of the different component processes, including perceptual analysis,
construction and maintenance of a memory trace, retention of order information,
rehearsal, retrieval and redintegration. Another crucial capacity that undergoes a
similar striking development is complex working memory, the ability to manipulate
and store material simultaneously. Possible sources of age-related changes in working
memory include increases in processing efficiency and attentional capacity, and taskswitching. These two short-term memory systems might play significant but distinct
roles in supporting the acquisition of knowledge and skills during childhood. Whereas
phonological short-term memory is linked specifically with the learning of the
phonological structures of new words, complex working memory appears to support
processing and learning in a wide range of contexts, in both childhood and adulthood.
I
S.E. Gathercole is at
the Department of
Experimental
Psychology,
University of Bristol,
8 Woodland Road,
Bristol,
UK BS8 1TN.
tel:
+44 117 928 8449
fax:
+44 117 928 8588
e-mail: sue.gathercole
@bristol.ac.uk
410
n the course of our everyday activities, we often have to hold
in mind relatively meaningless information for short periods of
time. Common situations include remembering verbal material, such as a postcode, a telephone number or the spelling of
an unfamiliar name for sufficiently long to be able to write it
down, or carrying out complex arithmetic calculations that involve mental storage of the intermediate products of our computations. This flexible capacity to store and manipulate information, termed ‘short-term memory’ or ‘working memory’, is
extremely important to our effective cognitive functioning.
Holding information in memory in this way is effortful,
attention-demanding and highly prone to failure, particularly when the information load or other cognitive demands
placed on the rememberer are high. One of the most powerful factors influencing short-term memory capacity is age. The
short-term memory abilities of children increase markedly
up to adolescence, with typically a two- to three-fold expansion in memory capacity occurring between four and 14 years
of age (see Box 1).
Despite the degree of consistency in developmental functions across different measures, there is little compelling evidence from adult data that a single memory system underpins
all aspects of short-term memory performance. Findings from
behavioural studies of normal adults, from neuropsychological
investigations of individuals with acquired brain damage, and
from neuroimaging studies of regions of brain activity associated with different short-term memory tasks, indicate that
anatomically and functionally distinct systems serve the
temporary storage and rehearsal of phonological (verbal) and
visuospatial material1,2. These storage-based memory systems
have themselves been distinguished from more flexible capacities to engage in many storage, processing, inhibition,
and retrieval processes in complex cognitive activities such as
language comprehension, mental arithmetic, and reasoning3–5.
These different components of short-term memory are
associated with activity in different brain regions (Box 2).
According to the Baddeley and Hitch model of working
memory6, the storage of limited amounts of either verbal or
visuospatial material is mediated by domain-specific ‘slave’
systems, the phonological loop7 and the visuospatial sketchpad8. The capacity to perform more complex memory activities that include a substantial processing component are
ascribed to the central executive9, a limited capacity system
responsible for several functions including the storage and
retrieval of information, directing the flow of information
through the short-term memory system as a whole, the control
of action, and planning.
There are several other significant theoretical perspectives
on complex working memory, too. It has been variously
characterized as (1) a system fuelled by a limited capacity
resource that can be flexibly deployed to support either
processing or storage3,10, (2) activated portions of long-term
memory controlled by an attentional resource with inhibitory capabilities11,12, or (3) a short-term memory mechanism
providing cue-based access to long-term working memory
systems, which are organized around specialized retrieval
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Trends in Cognitive Sciences – Vol. 3, No. 11,
PII: S1364-6613(99)01388-1
November 1999
Review
Gathercole – Development of short-term memory
Box 1. Measuring short-term memory capacity
References
a Gathercole, S.E. and Baddeley, A.D. (1996) The children’s test of non-word
repetition, The Psychological Corporation, UK.
b Gathercole, S.E. and Baddeley, A.D. (1996) The non-word memory test (available
from the authors on request)
c Isaacs, E.B. and Vargha-Khadem, F. (1989) Differential course of development of
spatial and verbal memory span: a normative study Br. J. Dev. Psychol. 7, 377–380
d Siegel, L.S. (1994) Working memory and reading: a life-span perspective Int. J. Behav.
Dev. 17, 109–124
e Gathercole, S.E. and Pickering, S.J. Assessment of working memory in six- and
seven-year old children J. Educ. Psychol. (in press)
f Wilson, J.T.L., Scott, J.H. and Power, K.G. (1987) Developmental differences in the
span of visual memory for pattern Br. J. Dev. Psychol. 5, 249–255
g Diamond, A. et al. (1997) Prefrontal cortex cognitive deficits in children treated
early and continuously for PKU Monogr. Soc. Res. Child Dev. 62
1.6
Performance (proportional score)
A variety of methods have been devised to assess short-term memory capacity. Examples of some of those most commonly used with children are shown
in Table I. In each case, the response involves recalling information presented
for a brief period and that is not physically present at the time of recall. A common feature of many methods, which make them particularly suitable when
working with children, is the use of a span procedure in which the amount of
material to be remembered is increased over successive trials. This is typically
achieved by progressively increasing the number of elements to be remembered until memory performance falls below a criterion level of accuracy.
Memory span is then defined as the maximum amount of information that
an individual can remember accurately.
Changes in performance on some measures of short-term memory during
childhood are shown in Fig. I, in which mean performance of each age group
(on which data are available) is expressed as a proportion of mean performance of nine-year-old children. Each of these measures taps either phonological short-term memory, visuospatial short-term memory, or complex working
memory (see main text for explanation of these terms).
Generally, memory performance increases steeply up to eight years of age,
and shows more gradual improvement thereafter to asymptotic levels at 11
or 12 years. The exception to this profile is listening span (Ref. d), a complex
measure of working-memory span that shows a constant steep developmental
slope extending up to 16 years of age. This indication that complex working
memory may undergo a longer period of development than phonological and
visuospatial short-term memory is consistent with the lengthy time course of
the development of the frontal lobes, the principal brain region associated
with complex working-memory capacities (discussed in Box 2).
1.4
1.2
1.0
0.8
0.6
0.4
2
4
6
8
10
12
14
16
Age
trends in Cognitive Sciences
Fig. I. Performance on measures of short-term memory as a function
of age. Mean performance of each age group is plotted as a proportion of
mean performance of nine-year olds. Blue squares, digit span (phonological
memory); red triangles, non-word repetition (phonological memory); open
circles, forward digit span; green squares, Corsi blocks (visuospatial memory);
yellow triangles, listening span (complex working memory); filled circles,
backward digit span (complex working memory). All data are redrawn from
the following: non-word repetition, Refs a,b; forward digit span, backward
digit span, and Corsi blocks, Ref. c; listening span, Ref. d.
Table I. Tasks commonly used to assess short-term memory (STM) abilities in children
Type of STM
Method
Examples of stimulia
Correct response
Ref.
Phonological
Digit span
8…5…2
“8 … 5 … 2”
c
Recall of words
chin … led … bag
“chin … led … bag”
e
Nonword repetition
woogalamic
“woogalamic”
a
Visuospatial
Pattern recall
f
(3)
(1)
Corsi blocks
Working memory/
(3)
(1)
(2)
Listening span
executive processes
Oranges live in water
“no”
Pigs have curly tails
“yes … water, tails”
Counting span
Backward digit span
Day/night Stroop
(2)
9…2…5
c
e
“4,3”
e
“5,2,9”
c
“day”
g
a Stimuli printed in italics are either verbally presented or represent experimenter actions (arrows). Actions are pointing actions, with positions of
correct pointing responses in sequence shown in parentheses where relevant to the task.
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Box 2. The neuroanatomy of short-term and working memory
4
6
9
3 5
1
2
46
43 41
8
7
40
10
45
47
11
39
19
18
44
52
38
17
22 42
21
37
19
underpinning the prefrontal cortex (Ref. f). Rather less is known about the
possible developmental changes in the brain systems underpinning phonological and visuospatial short-term memory, and about non-inhibitory aspects
of more complex working-memory capacities, such as retrieval and activation
of information from long-term memory. (The development during infancy
and childhood of the brain systems underpinning human memory is discussed
further in Ref. g.)
References
a Kalat, J.W. (1995) Biological Psychology (5th edn), Brooks/Cole Publishing Co.
b Elman, J.L. et al. (1998) Rethinking Innateness, MIT Press
c Smith, E.E. and Jonides, J. (1998) Neuroimaging analyses of working memory Proc.
Natl. Acad. Sci. U. S. A. 95, 12061–12068
20
trends in Cognitive Sciences
Fig. I. Sagittal view of the adult brain, with Brodmann areas marked.
The four major lobes are demarcated by colour: frontal (yellow), parietal
(green), temporal (red), and occipital (blue).
d O’Reilly, R., Braver, T.S. and Cohen, J.D. (1999) A biologically based computational
model of working memory, in Models of Working Memory (Miyake, A. and Shah, P.,
eds), pp. 375–411, Cambridge University Press
e Diamond, A. (1990) Developmental time course in human infants and infant
monkeys, and the neural bases, of inhibitory control in reaching, in The Development
The cerebral cortex is divided into four lobes: frontal (Fig. I, shown in yellow),
parietal (green), temporal (red), and occipital (blue).
The basic neuroanatomical structure of the child’s brain is in place at birth
(Ref. a). Brain mass increases threefold to about 1000 g between birth and
12 months (the mass of the adult brain is 1200–1400 g), primarily as a consequence of the development of cortical structures. Adult levels of brain metabolism are attained by 10 months of age and increase beyond this, to maximum
levels at four years of age, when they reach 150% of adult activity. Rates of
metabolic change vary according to cortical region: activity in the temporal,
parietal and occipital lobes reaches adult levels between three and six months of
age, whereas frontal lobe metabolic activity increases, and structural development starts, later – at around nine months – and continues into early adolescence (Ref. b). Another key developmental feature is the rapid growth in the
number of synaptic connections within and across the cortex, which peaks in
the second year of life. From four years of age through to adolescence, there
is a slow decline in both synaptic density and brain metabolism.
Advances in neuroimaging techniques such as PET and functional MRI in
recent years have led to the identification of distinct cortical brain structures
underpinning the principal components of short-term and working memory
in normal adults. The neuroanatomical loci of some of these components are
summarized in Table I.
The extent to which the neural circuitry of short-term memory in the adult
brain corresponds to that of the developing child is not fully understood.
Work by Diamond and colleagues has established that the relatively late
development of the prefrontal cortex closely parallels the time course of inhibitory aspects of executive function, such as the ability to suppress prepotent
responses (Ref. e). This group has also demonstrated marked deficits in executive capacities in children with impairments of the neurotransmitter system
and Neural Bases of Higher Cognitive Functions (Diamond, A., ed.), Ann. New York
Acad. Sci. 608, 394–426
f Diamond, A. et al. (1997) Prefrontal cortex cognitive deficits in children treated early
and continuously for PKU Monogr. Soc. Res. Child Dev. 62
g Nelson, C.A. (1995) The ontogeny of human memory: a cognitive neuroscience
perspective Dev. Psychol. 31 723–738
Table I. Regions of cortical activity associated
with short-term memory
Type of shortterm memory
Cortical areas
Hemisphere Brodmann
areas
Posterior paretial
Broca’s area,
premotor cortex,
supplementary
motor cortex
Left
Left
Left
40
44, 6
6
Spatiald
Storage
Rehearsal
Inferior prefrontal
Anterior occipital,
posterior parietal
premotor cortex
Right
Right
Right
47
19, 40
6
Working
memory/
executive
processesc,d
Dorsolateral
prefrontal cortex
Left/
bilateral
9, 10, 44,
45, 46
Phonologicalc
Storage
Rehearsal
structures13. Major issues that divide theorists include the
domain-specificity of working memory14,15, and the extent
to which capacity limitations arise from processing skills16
or other resources, such as controlled attention11.
Each of the major domains of short-term memory shows
a steep developmental function through childhood (Box 1).
This article focusses on current debates and advances in understanding the development and everyday function of two of
these aspects of short-term memory: phonological short-term
memory and complex working memory.
Developmental changes in phonological short-term memory
Research on adult memory has identified many distinct
processes involved in remembering verbal information over
short periods of time (see Box 3). To pinpoint the source or
sources of improved phonological memory performance with
age, it is necessary to apply specialized empirical methods
that allow the isolation of individual processes. Below, evidence is summarized for development in each of these specific
short-term memory processes.
Perceptual analysis
The early processes of perceptual encoding of the speech signal must be successfully completed in order to yield a phonological memory trace. It has been suggested that developmental changes in performance on phonological memory
measures may be indirect consequences of basic perceptual
analytic abilities17,18. Subtle acoustic processing deficits do not,
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Gathercole – Development of short-term memory
Review
Box 3. What is involved in phonological short-term storage?
The complexity of the short-term retention of phonological material is illustrated
in Fig. I, which traces some of the various processes involved in recalling a
three-digit sequence. These processes are described in more detail below.
trieval process appears to be a rapid, serial scanning process (Ref. g). In order
to retrieve items in the correct sequence, original temporal context may be
reinstated to help retrieve associated item information (Ref. e).
Acoustic storage
The acoustic record of the most recent auditory speech item is stored in a sensory
form that preserves its physical features, and is highly vulnerable to disruption
by subsequent speech material (Ref. a).
Redintegration
Stored knowledge relating to the lexical, semantic and phonological properties of specific items and of the language more generally is used to reconstruct incomplete phonological traces in a process termed redintegration
(Refs h,i). These reconstructive processes can occur either during storage or
at retrieval.
Phonological analysis and storage
The phonological structure of the to-be-remembered material is analysed from
the sensory signal via the processes of perceptual analysis and segmentation.
The resulting phonological specification is stored in phonological short-term
memory. Information is lost both during presentation and recall through
decay and, possibly, interference (Refs b,c).
Temporal order
The temporal context of the memory items must be coded for accurate serial
memory. Possible mechanisms for recording the sequence information to be
associated with individual items include activation gradients that diminish for
successive items in a sequence (Ref. d), dynamic item context that changes
across time (Ref. e), and oscillators operating at different frequencies (Ref. f).
References
a Frankish, C.R. (1996) Auditory short-term memory and the perception of speech,
in Models of Short-Term Memory (Gathercole, S.E., ed.), pp. 179–208, Psychology
Press
b Cowan, N. et al. (1992) The role of verbal output time in the effects of word length
on immediate memory J. Mem. Lang. 31, 1–17
c Neath, I. and Nairne, J.S. (1995) Word length effects in immediate memory:
overwriting trace-decay theory Psychonomic Bull. Rev. 2, 429–441
d Page, M.P.A. and Norris, D.G. (1998) The Primacy Model: a new model of immediate
serial recall Psychol. Rev. 105, 761–781
e Burgess, N. and Hitch, G.J. (1992) Toward a network model of the articulatory loop
J. Mem. Lang. 31, 429–460
f Brown, G.D.A. et al. The development of memory for serial order: a temporal-
Rehearsal
One way that phonological material can be maintained for longer periods
within this system is via covert rehearsal, a serial process that appears to refresh
the decaying phonological representations.
contextual distinctiveness model Int. J. Psychol. (in press)
g Cowan, N. et al. (1998) Two separate verbal processing rates contribute to shortterm memory span J. Exp. Psychol. Gen. 127, 141–160
h Hulme, C. et al. (1997) Word-frequency effects on short-term memory tasks:
evidence for a redintegration process in immediate serial recall J. Exp. Psychol.
Learn. Mem. Cognit. 23, 1217–1232
i Gathercole, S.E. et al. (1999) Phonotactic influences on short-term memory J. Exp.
Psychol. Learn. Mem. Cognit. 25, 84–95
Presentation
Spoken presentation
Retrieval
“eight … five … two”
Acoustic traces
Phonological traces
/eIt/
/fiv/
/t u:/
/eIt/
/fiv/
/t u:/
/eI*/
/*i*/
/t u:/
Phonological traces
(*information lost through
decay or interference)
trends in Cognitive Sciences
Retrieval
Stored information needs to be accurately retrieved. A crucial step in the re-
Temporal context
Rehearsal
Serial access to phonological
traces guided by reinstated
temporal context
/eIt/
/nin/
/t u:/
“eight … nine … two”
Letters underlined reflect the use
of stored knowledge to re-integrate
incomplete traces
Spoken output
Fig. I. Some of the processes involved in recalling a three-item digit sequence. In this example, the phonological structure of each item in the auditory digit
sequence 8, 5, 2 is successfully encoded in a memory trace, is associated with its temporal context (indicated by bi-directional arrows linking each trace to its temporal
context, represented here as a moving clock face), and is accurately rehearsed. The traces are retrieved (right) by reinstating the original temporal context and accessing the associated phonological trace. By this point in time, however, some phonological information has been lost from the traces corresponding to two of the items
(8 and 5), although the final item (2) is intact. The remaining partial information is sufficient to support the correct redintegration of the initial item (8) owing to its
phonological redundancy within the possible stimulus set (it is the only single-digit number that commences with the vowel sound eI). However, the remaining vowel
information in the trace for the middle list item (5) is incorrectly reconstructed as 9. The resulting recall attempt consists of correct recall of the first and last items, with
an item error in the middle list position.
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however, appear to lie at the root of the very poor non-word
repetition performance of at least one group, children with
specific language impairment (SLI). In a twin study, Bishop
et al. assessed the abilities of children with SLI to perform two
tasks: non-word repetition, and the fine-grained temporal
discrimination of brief tones19. The SLI group performed at
low levels on both tasks. However, non-word repetition scores
were not strongly associated with the temporal discrimination measures, and whereas the former measure yielded
strong heritability estimates, the latter did not. Thus, in this
population at least, early perceptual skills do not strongly
constrain non-word repetition abilities.
Sensory memory
The presentation of auditory speech information results in
two parallel, temporary memory traces, one sensory and one
phonological in nature. Older children show some evidence
of both increased capacity and persistence of auditory sensory
memory20,21.
Phonological storage
The phonological features of memory items are represented
in a form that is less vulnerable to overwriting than auditory
sensory memory, but that nonetheless decays over a matter
of seconds. According to the working-memory model6, these
traces are held in the phonological short-term store component of the phonological loop, where they are subject to
decay if unrehearsed7. It has been argued, alternatively, that
interference rather than decay is the main mechanism for
loss of information from temporary phonological storage22.
Possible sources for developmental changes in phonological
storage include changes in rates of decay and the quality of
the encoding23.
Memory for order
It is necessary to retain the order as well as the content of individual items if a sequence of verbal items is to be recalled
correctly. Pickering, Gathercole and Peaker found little evidence for differences in the retention of order information
between five and eight years of age, although recall accuracy
was substantially greater in the older age group24. Both groups
showed similar profiles of serial-order errors, with migrations of
items over short distances in the recall protocol predominating.
Differences in order memory beyond eight years of age were,
however, found in another unpublished study by McCormack
et al. (cited in Ref. 25). Older children and adults produced
relatively fewer movement errors than eight-year-olds, and
order errors spanned shorter distances from the target position
in these older age groups. Brown et al.25 simulated these developmental changes by increasing the effectiveness in older age
groups of the learning context used to maintain serial-order
information in an oscillator-based model of serial recall26.
Subvocal rehearsal
Children below about seven years of age do not spontaneously
re-code visual stimuli into verbal form for temporary storage27,
or actively rehearse auditory speech material28,29. After that
age, however, a large component of the age-related change
in memory span is closely linked to increases in the rate of
subvocal articulation30. One explanation for this finding is
that increased rehearsal rates lead to better prevention of
decay of temporary memory traces, and hence to greater
memory span31. Similarly, faster articulation rates might lead
to decreased decay during spoken recall32.
Retrieval
Another rate-based process that might contribute to the developmental memory function is the rapid, serial retrieval of
memory traces prior to output. Cowan et al. reported that
estimates of retrieval rate based on pauses during recall accounted for substantial age-related variance in memory span
in children aged between seven and 11 years, with older children showing faster rates30. Estimated rates of rehearsal and
retrieval in this study were not associated with one another,
and both were independently linked with memory span, indicating that age-related changes in immediate memory
cannot be adequately explained in terms of an increase in a
single rate of processing, as some authors have argued33,34.
Redintegration
The use of long-term knowledge to reconstruct partial phonological traces of long-term knowledge may become increasingly effective in older children35, although it is apparent that
by six years of age, substantial reconstruction of partial memory traces is already taking place on the basis of both lexical
and phonotactic information36. Further investigation of developmental changes in reconstructive memory processes is
required to evaluate their precise contribution to age-related
changes in memory span.
Summary
The substantial improvement in phonological storage capacities over the childhood years appears to have its origin
in multiple component processes, many of which occur in
parallel. The extent to which the sum of the individual
sources of development identified so far can adequately capture the developmental changes observed at the global level
of memory performance is, however, difficult to assess in the
absence of a detailed model that specifies all key processes
and their inter-relationships. One important approach that is
likely to advance this more general understanding of shortterm memory development is the application of computational models of short-term memory function. Several computationally explicit accounts of immediate verbal memory
have been advanced in recent years that have proved to be capable of accommodating core features of short-term memory
performance37–39. The simulation of developmental changes
in these models will provide a significant step towards integrating the detailed empirical evidence already available into
a coherent and more complete theoretical framework of adult
short-term memory and its developmental origins.
Does phonological short-term memory support new
word learning?
Why do children need the capacity to store phonological material for short periods of time? And, given the sizeable differences across age groups and between individuals of the same
age in phonological memory capacity, what are the consequences for a child with relatively weak phonological memory skills? One claim has been that phonological short-term
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A
Phonological
short-term memory
Non-word
repetition
B
Vocabulary
growth
Review
Improved non-word
repetition
Segmented lexical
representatives
Phonological
long-term memory
trends in Cognitive Sciences
Fig. 1. Two models of the processes underpinning non-word repetition performance. Thicker arrows denote stronger links between
items. (A) In this model, phonological storage supports non-word repetition and long-term phonological learning. (B) An alternative model
proposes that non-word repetition is indirectly boosted by vocabulary growth.
storage plays a highly specific role in supporting the acquisition of new vocabulary, based on evidence that phonological
memory skills are closely associated both with existing vocabulary knowledge and with the ease of acquiring new words
in either native or foreign languages5,40–46. Consistent with this
view, children with specific language impairment40, which
is characterized by unexpectedly poor language learning, have
severely impaired capacities for phonological short-term
storage47.
Particularly close links occur between the long-term
phonological learning component of vocabulary acquisition
and one task believed to tap phonological short-term memory,
non-word repetition40. For example, Gathercole et al. assessed
the non-word repetition and digit recall abilities of a large
group of five-year-old children who were also tested on a range
of standardized measures of vocabulary knowledge and four
word learning tasks48. In three of the learning tasks, the child
attempted to learn an association between unfamiliar phonological structures. In the remaining task, the association to be
learned was between two words that were already familiar to
the child. Non-word repetition scores were closely related to
vocabulary scores (with correlation coefficients ranging from
0.51 to 0.60), to scores on the three non-word learning tasks
(correlation coefficients ranging from 0.46 to 0.51), but not
to the word-word learning task (correlation coefficient 0.16).
Digit recall scores showed significant but generally weaker
associations with the vocabulary measures.
The causal basis of the link between non-word repetition
and vocabulary knowledge has been the focus of considerable
debate17. Two current accounts are presented in diagrammatic form in Fig. 1. According to one account (Fig. 1A),
non-word repetition provides a more sensitive measure of
phonological short-term memory capacity than measures such
as digit recall, because of the absence of any stored lexical specification of the phonological structure of a non-word. As a
result, the child cannot use long-term representations to supplement recall and has to rely largely on phonological shortterm memory49, possibly aided by some long-term phonotactic knowledge50. Thus, the relationship between non-word
repetition and vocabulary knowledge arises principally because temporary phonological traces of spoken non-words are
used as a basis for constructing stable long-term representations of the sound structures of familiar words, a process
that typically occurs over many exposures to a new word40.
An alternative view is that cognitive processes or mechanisms other than phonological short-term memory, such as
the analytic procedures that extract a phonological description
from the incoming acoustic speech signal, lie at the root of the
link between non-word repetition and vocabulary learning.
There are several findings that are consistent with this position: children who score poorly on non-word repetition show
reduced brain responses to phonemic contrasts51, training in
phonological awareness boosts both non-word repetition
ability and phonological segmentation skills52, and vocabulary knowledge shares close links with phonological segmentation ability as well as non-word repetition skills17,41,53.
On the basis of this evidence, Metsala has proposed that vocabulary growth may be the prime causal mechanism in the
developmental relationship between phonological processing
and phonological short-term memory measures (Fig. 1B)18.
As vocabulary size increases during the early childhood years,
the child shifts from relying on wholistic representations
and analysis of familiar words towards a more analytic segmental approach that recognizes the phoneme as a basic unit
of language54. Metsala argues that, via this process of lexical
restructuring, ‘more segmented lexical representations will
lead to better flexibility in arranging individual phonemes
in new patterns and thus more robust representation of
non-words’ (Ref. 18, p. 6).
The debate concerning the dynamic basis of links between vocabulary knowledge and a range of phonological processing skills including short-term memory is difficult to resolve on the basis of developmental associations alone, owing
to problems in identifying patterns of causality from correlational data. Interpretational ambiguity is further exacerbated
by the overlap in processes involved in typical phonological
segmentation and phonological short-term memory tasks.
The impact of perceptual analysis on phonological short-term
storage has already been considered. Equally, conventional
phonological processing and segmentation tasks themselves
place a substantial phonological storage burden upon the
child. Thus, neither class of task purely reflects one or other
set of processes.
Using different experimental methodologies has provided
a useful means of teasing apart the phonological processing
from the phonological storage component of short-term memory. Variables known to disrupt the operation of phonological
short-term memory (such as articulatory suppression, word
length, and phonological similarity) have been shown to impair the phonological learning of non-words whilst leaving
word–word learning relatively intact55,56. As these variables
seem unlikely to influence the initial phonological processing
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Gathercole – Development of short-term memory
of the memory items, this evidence favours model A over
model B (Fig. 1).
Summary
Phonological short-term memory abilities in children show
close links with their capacity to learn new words in the language, although the causal basis of the relationship is still open
to debate. One view is that temporary phonological storage
is a crucial step in the construction of stable long-term phonological representations of new words, so that phonological
memory skills provide a crucial constraint in word learning.
An alternative account is that the relationship between phonological memory and vocabulary learning is secondary, mediated by a more direct link between segmental analysis and the
construction of the phonological lexicon. Disentangling associated from causal connections in developmental contexts is
particularly difficult, as basic skills such as phonological segmentation and phonological memory are rarely dissociable
from one another in normal development. Resolution of current theoretical conflicts may require shifts towards new experimental methods that allow different processes to be functionally distinguished, and towards the study of neuropathological
cases in whom marked dissociations can be found.
Developmental changes in complex working memory
Two principal theoretical frameworks have been used to
characterize the development of working memory. The major
distinction between these frameworks is the extent to which,
either the processing demands of specific activities, or a general capacity for controlling attention, are viewed as imposing
the major constraint on working-memory capacity.
Trade-off between processing and storage
According to Daneman, Carpenter and their colleagues,
working memory is fuelled by a limited-capacity processing
resource that can be flexibly allocated to meet the processing
and storage demands of complex cognitive activities3,10. Thus,
in tasks in which processing and storage demands exceed the
available capacity, there will be a trade-off between processing
and storage activities: the greater the resource devoted to
ongoing processing, the less will be available to dedicate to
storing the products of processing activities.
Using this framework, Case and colleagues proposed that
during the childhood years, the total amount of processing
resource available to support these activities remains constant
but the efficiency of processing activities increases57. Thus, as
the child grows older and becomes more skilled at processing
and manipulating information, the amount of resource required to support processing decreases, and memory storage
capacity increases.
This singular view of memory development as reflecting
different points in a trade-off function between processing and
storage has recently been challenged by Towse, Hitch and
Hutton58. They demonstrated that performance on complex
working-memory tasks that tap several knowledge domains
is strongly influenced by the time at which children must
store items in short-term memory, with increased memory
delay being associated with storage decrements. This feature
of memory performance cannot readily be accommodated by
a processing/storage trade-off account. Instead, it suggests
that age-related changes in task-switching behaviour and in
decay functions might be possible origins of the striking differences found in complex working-memory performance
at different times in childhood.
Controlled attention of the source of developmental differences
Another conceptualization of complex working memory emphasizes selective attention rather than processing efficiency
per se as the major constraint on task performance. Engle and
colleagues have argued that working memory consists of
domain-general controlled attention, which is applied to activated long-term memory structures, and which may be served
by the dorsolateral prefrontal cortex11,12. Findings of close
associations between estimates of working memory capacity
for different domains of activity14 are consistent with this view
that working memory performance is constrained by a single
general factor rather than by processing expertise in a particular
domain.
Although this framework has primarily been developed
and applied to the understanding of individual differences in
complex working memory rather than to development, there
is evidence for age-related changes in attention underpinning
the improved working memory capacities of older children.
Swanson conducted a large-scale study of individuals aged
from six to 57 years, in which working memory performance
was assessed under a variety of access, storage and processing
conditions, for both verbal and visuospatial material59. The
results showed that age-related changes in performance were
not specific to either verbal or visuospatial domains, and were
related to the memory access and storage demands of the activities rather than processing demands. Swanson argues on
this basis that amount of activation of long-term structures
changes with age, owing to increased availability of attentional
resources as children grow older.
It should be noted that the view that individual differences in complex working memory have their source in the
capacity of general controlled attention rather than in more
domain-specific processing and storage constraints is not
uncontentious. Evidence from other research groups points
to limitations in working memory capacity which are highly
specific to particular knowledge and processing domains15.
There is also concern about the extent to which contrasting
verbal and visuospatial tasks used in some studies truly tap
distinct underlying domains, and so have the power to test
the domain-specificity of working memory.
Summary
Age-related changes in complex memory have been conceived
principally as arising from changes, either in processing efficiency within a particular domain or in the capacity of controlled attention, in both cases based largely on correlational
evidence. New experimental techniques for identifying highly
specific processes contributing to complex memory span
may provide an important step towards resolving these fundamental differences, and in pinpointing more precisely the
origin of developmental changes.
The role of working memory in cognitive development
As complex working-memory tasks are typically devised to
mimic the competing mental demands of many of our
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Gathercole – Development of short-term memory
everyday activities, it is perhaps unsurprising that children’s
performance on these tasks has been found to be related to
attainments in many key intellectual domains as well as
measures of general intelligence11. Some specific hypotheses
concerning the contribution of working memory to the acquisition of skill and knowledge in some domains have,
however, been explored and are summarized below.
Working memory and arithmetic
One possibility that has been widely entertained is that the
development of mathematical ability is significantly constrained by working-memory capacity. The data, however,
are not particularly conclusive. While it is certainly the case
that working memory (as well as phonological short-term
memory) can play a crucial role in supporting on-line mental
arithmetic in both children and adults60,61, evidence that either
system is crucial to the acquisition of arithmetic ability over
the childhood period in general is far from consistent62,63. This
might reflect the fact that whereas working memory is important for components of mathematical ability such as mental
arithmetic, it may play a relatively minimal role in supporting the understanding of conceptual aspects of mathematics
that are crucial at other points in a child’s mathematical
education.
Working memory and language comprehension
Complex working memory and performance on tasks involving both the written and spoken comprehension of language
show robust and consistent associations in both children and
adults4,64. Recent evidence indicates that this is a genuine
causal link rather than a simple association11. Individuals with
good working-memory abilities are also particularly good at
acquiring the conceptual aspects of vocabulary acquisition5,65;
this contrasts with the specific links found between phonological short-term memory and the phonological aspects of
vocabulary learning.
Working memory and school achievement
In addition to the apparent involvement of working memory
in arithmetic processing and language comprehension across
the life span, adult studies have established links between
working-memory capacity and many intellectual abilities,
including following directions, note-taking, writing, reasoning and complex learning11. Given the range of important
everyday cognitive activities that appear to be constrained by
working memory, it seems reasonable to suppose that children with severely compromised working-memory capacities
will be educationally disadvantaged at school, experiencing a
range of learning difficulties. There is recent evidence that
this is indeed the case. Gathercole and Pickering found that
measures of complex working memory (but not phonological
short-term memory) were highly effective in identifying sixand seven-year-old children who were recognized by their
schools as having special educational needs arising from learning difficulties, and also in discriminating children whose
special needs were recognized more than a year after the
memory assessment66. In addition to providing support for
the contention that working memory is a key system in supporting learning in an educational context, these findings
suggest that working-memory assessments might provide a
Review
valuable means of identifying children at present and future
educational risk.
Summary
Working-memory capacity appears to constrain many different aspects of complex cognitive behaviour in both children
and adults. While the specific role played by working memory in the acquisition during childhood of knowledge and
skills in specific domains is not as yet fully understood, recent evidence suggests that poor working-memory capacity
can severely compromise a child’s abilities to make normal
educational progress.
Conclusion
The abilities to hold and manipulate information over short
periods of time undergoes substantial changes through the
childhood years, with estimates of maximum capacity almost
trebling in the period between the pre-school years and early
adolescence. Age-related changes in phonological short-term
memory appear to reflect increased efficiency in a whole range
of processes including the storage of item and order information, rehearsal, retrieval and reconstruction of memory
traces. Changes during childhood in complex working memory, on the other hand, have been attributed both to gains
in the efficiency of processing and to increased attentional
capacity in older children.
The two temporary memory systems can be further distinguished by the roles they play in supporting the acquisition of knowledge and skills. Whereas phonological shortterm storage appears to be a crucial step in learning the
phonological forms of new words, complex working-memory
skills appear to constrain achievement in a whole range of
learning domains including mathematics and language.
Outstanding questions
• Is there actually a functionally distinct system or set of systems serving
short-term memory? Some argue that temporary representations that
support performance on immediate memory tasks merely reflect
persistence of products within highly specific processing domains, such as
phonological processing. On this view, developmental changes in memory
performance through childhood arise from changes in the detailed
nature of the processing domains themselves rather than in ‘short-term
memory’. Neuropsychological dissociations between processing and
short-term memory nevertheless provide substantial justification for the
assumption of distinct storage mechanisms with different neuroanatomical
architectures.
• Computational models of short-term memory have been developed in
recent years that effectively simulate a wide range of key empirical
phenomena in adult short-term memory. Can we build much-needed
models of the development of short-term memory in order to provide
impetus to both theorizing and empirical investigation of short-term
memory during childhood?
• Visuospatial short-term memory appears to represent a distinct system,
but as yet relatively little is known about the ways in which adult capacities
to store and manipulate such non-verbal material emerge across the
childhood period.
• Neuroimaging techniques are currently being effectively applied to chart
the neuroanatomy of the brain systems underpinning the major
components of short-term memory in adults. Is the adult organization of
short-term memory function reflected in the child’s developing brain?
Evidence for reorganization of the brain systems underlying short-term
memory during childhood would provide very valuable clues to changes
in functional memory systems.
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November 1999
Review
Gathercole – Development of short-term memory
(Oaksford, M. and Chater, N., eds), pp. 165–193, Oxford University Press
Acknowledgements
27 Hitch, G.J. and Halliday, M.S. (1983) Working memory in children Philos.
The preparation of this work was supported by the Medical Research
Trans. R. Soc. London Ser. B 302, 324–340
Council of Great Britain.
28 Gathercole, S.E., Adams, A-M. and Hitch, G.J. (1994) Do young children
rehearse? An individual-differences’ analysis Mem. Cognit. 22, 201–207
29 Gathercole, S.E. and Hitch, G.J. (1993) Developmental changes in short-
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The role of gesture in
communication and
thinking
Susan Goldin-Meadow
People move their hands as they talk – they gesture. Gesturing is a robust phenomenon,
found across cultures, ages, and tasks. Gesture is even found in individuals blind from birth.
But what purpose, if any, does gesture serve? In this review, I begin by examining gesture
when it stands on its own, substituting for speech and clearly serving a communicative
function. When called upon to carry the full burden of communication, gesture assumes a
language-like form, with structure at word and sentence levels. However, when produced
along with speech, gesture assumes a different form – it becomes imagistic and analog.
Despite its form, the gesture that accompanies speech also communicates. Trained
coders can glean substantive information from gesture – information that is not always
identical to that gleaned from speech. Gesture can thus serve as a research tool, shedding
light on speakers’ unspoken thoughts. The controversial question is whether gesture
conveys information to listeners not trained to read them. Do spontaneous gestures
communicate to ordinary listeners? Or might they be produced only for speakers
themselves? I suggest these are not mutually exclusive functions – gesture serves as
both a tool for communication for listeners, and a tool for thinking for speakers.
P
eople gesture. This phenomenon has been remarked upon
for at least 2000 years, across domains as diverse as philosophy,
rhetoric, theater, divinity and language. The gestures that
are most salient to speakers, and to listeners, are the codified
(or conventionalized) forms that can substitute for speech.
There is, however, another type of gesture that people routinely produce – informal, non-codified hand movements,
fleetingly generated during the course of speaking. The content of these gestures is not typically the object of public
scrutiny. As a result, these speech-accompanying gestures
have the potential to reflect thoughts that may themselves be
relatively unexamined by both speaker and listener. This type
of gesture may thus reveal aspects of thought that are not seen
in other, more codified forms of communication. In this review, I examine both types of gestures – those that substitute
for speech, and those that accompany speech – with an eye
towards understanding the role each plays in communication.
Gestures that substitute for speech
Gestures that have meaning independent of speech, and can
occur on their own without speech, are known as ‘emblems’1.
Emblems have standards of form and can clearly be ‘mispronounced’. For example, imagine producing the North
American ‘okay’ gesture with the pinkie rather than the index
finger touching the thumb – the resulting handshape is not
recognizable as an ‘okay’. For the most part, emblems are
1364-6613/99/$ – see front matter © 1999 Elsevier Science Ltd. All rights reserved.
PII: S1364-6613(99)01397-2
Trends in Cognitive Sciences – Vol. 3, No. 11,
November 1999
Susan GoldinMeadow is at the
Department of
Psychology,
University of
Chicago, 5730 South
Woodlawn Avenue,
Chicago, IL 60637,
USA.
tel: +1 773 702 2585
fax: +1 773 702 0320
e-mail: sgsg@ccp.
uchicago.edu
419